This core unit is located within the administrative offices at the Blood Research Institute, the research arm of the Blood Center of Southeastern Wisconsin. The BRI includes the offices and laboratories of the pediatric hematology faculty of the Department of Pediatrics at MCW, and is the location of the Comprehensive Center for Bleeding Disorders. This administrative core will coordinate this multifaceted program and consists of two major components. The first is providing the administrative coordination scientific leadership to the project leaders and their coinvestigators. It will utilize both an Executive Committee and an External Advisory Committee to guide this function as described in greater detail in the introduction to this program project. Two meetings a year will be organized for the Pi's and co-Pi's as well as the Directors of the primary clinical centers. One of these will be a brief one half-day meeting held in conjunction with the American Society of Hematology meeting in December of each year and the second will be a two day meeting held in Milwaukee for the investigator group of this PPG. A second major task of this administrative core is to provide a central site for receiving patient samples from the Primary Clinical Centers as well as their data entry forms. Core A will oversee data entry, quality control and validation of data from the primary (and secondary) clinical centers. These will be described separately.